Actinomycin D inhibition of monoclonal antibody binding to nucleolar phosphoprotein 37/5.2 (B23)

Actinomycin D was found to block binding of a monoclonal antibody to nucleolar phosphoprotein 37/5.2 (B23) when incubated either simultaneously with or prior to addition of the antibody. Daunorubicin had no significant blocking activity of this antigen-antibody reaction. In comparative studies with a monoclonal antibody to nucleolar phosphoprotein 110/5.2 (C23), actinomycin D exhibited little blocking activity. When a 42-mer peptide containing the epitope of protein 37/5.2 (B23) was tested as the antigen, similar inhibition by actinomycin D of binding of the monoclonal antibody was found. These results provide evidence for binding of actinomycin D to a specific epitope of protein 37/5.2 (B23).